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Microbial transformations of nitrification and denitrification are the main sources of nitrous oxide (N2O) from soils. Relative contributions of both processes to N2O emissions were estimated on an agricultural soil using 15N isotope tracers (15NH4+ or 15NO3-), for a 10-day batch experiment. Under unsaturated and saturated conditions, both processes were(More)
The variability of structures supporting tissue oxygen transport (capillaries) and oxygen consumption (mitochondria) was analyzed in skeletal muscles of wildebeest and dik-dik. Regional differences in mitochondria and capillary densities within individual muscles were found for M. semitendinosus (twofold) but not for M. longissimus dorsi and diaphragm.(More)
Constitutive heterochromatin comprising the centromeric and telomeric parts of chromosomes includes DNA marked by high levels of methylation associated with histones modified by repressive marks. These epigenetic modifications silence transcription and ensure stable inheritance of this inert state. Although environmental cues can alter epigenetic marks and(More)
The relationship between capillary density and mitochondrial volume density in skeletal muscle tissue is investigated on 25 African mammals ranging in body mass from 0.4 to 251 kg. As a general trend higher capillary densities, NA (c,f) are found in muscles with higher volume densities of mitochondria, Vv(mt,f). The individual data however show considerable(More)
The accurate estimation of stereological parameters defined on anisotropic structures is a long-standing problem. In this paper we seek to estimate the capillary length density JV in skeletal muscle tissue. A well-known model for directional anisotropy in space, namely the 'spherical normal' or 'Fisher axial distribution' model, is found to fit the relevant(More)
Maintenance of CG methylation ((m)CG) patterns is essential for chromatin-mediated epigenetic regulation of transcription in plants and mammals. However, functional links between (m)CG and other epigenetic mechanisms in vivo remain obscure. Using successive generations of an Arabidopsis thaliana mutant deficient in maintaining (m)CG, we find that (m)CG loss(More)
Transcriptional activity and structure of chromatin are correlated with patterns of covalent DNA and histone modification. Previous studies have revealed that high levels of histone H3 dimethylation at lysine 9 (H3K9me2), characteristic of transcriptionally silent heterochromatin in Arabidopsis, require hypermethylation of DNA at CpG sites. Here, we report(More)
An evaluation is made of the relative efficiency (precision of the final estimate per unit time of measurement on a given set of sections) of different methods for planar analysis aimed at estimating aggregate, overall stereological parameters (such as VV, SV). The methods tested are point-counting with different densities of test points (4 less than or(More)
Since O2 is mainly consumed in muscle mitochondria during heavy physical work, one would expect to find a relationship between the volume density of mitochondria in skeletal muscles and maximal O2 uptake. We analyzed the volume density of mitochondria, Vv(mt,f) in four muscles of a series of African mammals ranging in body mass from 0.4 to 251 kg. Vv(mt,f)(More)
The heterochromatic regions around centromeres of animal and plant chromosomes are composed of tandem repetitive sequences, interspersed with transposons and transposon derivatives. These sequences are largely transcriptionally silent and highly methylated, and are associated with specifically modified histones. Although embedded in heterochromatin,(More)